Proximity-sensing devices are sensor devices configured to detect presence of nearby objects without physical contact. Proximity-sensing devices are commonly used in electronic gears that will turn power-consuming circuitry on or off in response to the proximity-sensing devices detecting an object, person, or the like nearby. Use of proximity-sensing devices in such applications may be particularly efficient because they may provide for detecting proximity without having to make physical contact. Proximity-sensing devices may also be used in mobile phone, digital photo frames, television, or other electronic devices.
Generally, a proximity-sensing device has an emitter die and a receiver die. The radiation emitted from the emitter die is usually directed to an external object or an external medium before being received by the receiver die. In response to the radiation detected, the receiver die may generate a signal indicative of at least one property of the external object. For example, for proximity-sensing devices, the signal generated by the receiver die is indicative of presence of the external object within a predetermined distance of the proximity-sensing device.
However, on some occasions where a proximity-sensing device is attached within a transparent casing, a portion of the radiation reflected by the transparent casing may be detected by the receiver die without being reflected by the external object. The radiation detected by the receiver die without being redirected by the external object is often referred to as crosstalk. Crosstalk is independent of the external object and may reduce the signal-to-noise ratio of the proximity-sensing device.
Most proximity-sensing devices available in the market today are designed such that the emitter die and the receiver die are optically isolated. While this reduces crosstalk, detection of a close object such as an object touching the casing or in very close proximity with the proximity-sensing device may not be detected resulting in a blind zone. Designing a proximity-sensing device having minimum crosstalk and capability to detect zero distance objects may be challenging, but such proximity-sensing devices are in high demand. For example, most mobile phone requires a proximity-sensing device that is capable of detecting external object without a blind zone. Unlike the traditional use of proximity-sensing devices in automobile or other home appliances where proximity-sensing devices with blind zones are tolerated, a mobile phone may be held close enough or even touching the user and therefore, proximity-sensing devices for the modern mobile devices are required to detect external objects even at zero distance.